1. Field of the Invention
The present invention concerns the field of power electronics, in particular that of semiconductor diodes. It relates to a process for fabricating a semiconductor component according to the preamble of patent claim 1, and to a semiconductor component according to the preamble of patent claim 5.
2. Discussion of Background
One important parameter for the mode of operation of a semiconductor component is its axial carrier lifetime. This should, on the one hand, be as long as possible in order to keep the on-state losses small, but it should also be as short as possible in order to obtain a rapid blocking capability. For each semiconductor component, it is therefore necessary to find an optimum compromise in terms of its carrier lifetime. In order to achieve this, semiconductor components are provided with one or more defect regions or recombination regions, by means of which the carrier lifetime can be adjusted in a controlled way.
Generation of defects, and therefore adjustment of the axial carrier lifetime in semiconductor power components can basically be obtained in three ways: by irradiation with electrons, by doping with heavy metals, in particular with platinum or gold, or by particle irradiation with energetic heavy particles, in particular with hydrogen or helium nuclei.
Irradiation with electrons has the disadvantage that the semiconductor substrate is provided with defects throughout its volume, which does not permit an ideal compromise between the on-state behavior and the turn-off behavior of the semiconductor component. It is admittedly possible, by means of doping with heavy metals, to produce defects only in a predetermined region of the substrate. However, this process is elaborate and expensive.
One technique permitting controlled adjustment of the carrier lifetime which has now become established is particle irradiation with energetic heavy particles, protons or helium nuclei generally being used. Such a particle beam is directed at a surface of the semiconductor substrate, so that the particles penetrate into the substrate and produce defects there. The penetration depth of the particles depends in this case on their energy and the material composition of the matter to be penetrated. By selecting the particle energy, it is theoretically possible to determine the penetration depth in advance and therefore accurately adjust the position of the defect region. However, since semiconductor components do not generally have a homogeneous structure, the individual particles are exposed to different conditions.
This problem arises especially in the case of a semiconductor diode. Such a diode is represented in FIG. 1. Metal layers, which form an anode terminal 3 and a cathode terminal 4, are present on two opposite surfaces of a semiconductor substrate 1. The anode terminal 3 is in this case surrounded by passivation 2 in order to avoid edge effects, in particular charged interfacial states. Since the defect regions are intended to lie next to the anode 11, the irradiation must be carried out on the anode side. As can be seen in FIG. 1, a corresponding particle beam P therefore penetrates the metal layer 3 or the passivation 2, respectively, in order to enter the substrate 1. In this case, the metal layer and the passivation exert different breaking effects on the particles in the particle beam, so that the particles do not come to rest at the same depth. Instead, a defect region 5 is obtained which does not extend parallel to the surface on the anode side, but has a step 50 toward the edge. However, this nonuniform penetration depth of the particles, and the stepped defect region which results from this, impairs the functional capability of the diode. Since the edge is the most critical area of the diode, the effect of this shortcoming is made even greater.
Another disadvantage is that, when it penetrates the passivation, the particle beam produces defects in this area as well, in particular with covalent bonds being broken. Charged states are thus created both in the passivation and at the interface with the semiconductor, which reduce the maximum blocking capability of the diode.
Accordingly, one object of the invention is to provide a novel process for fabricating a semiconductor component, and a novel semiconductor component of the type mentioned at the start, which eliminate the disadvantages mentioned above.
This object is achieved by a process with the features of patent claim 1, and by a semiconductor component with the features of patent claim 5.
Other advantageous variants of the process and advantageous refinements can be found in the dependent patent claims.
According to the invention, in the fabrication process for the semiconductor component, the particle irradiation is carried out before the application of the metal layer and of the passivation. All the particles in the particle irradiation therefore encounter the same conditions, so that they penetrate to the same depth in the semiconductor substrate.
The process according to the invention makes it possible to fabricate a semiconductor component with a defect region that is continuous even in the edge areas. In this case, the position of the defects important for adjusting the carrier lifetime does not depend on the thickness and composition of the passivation and/or metallization. In addition, the passivation is protected from damage because it is not applied until after the particle irradiation.
The selection of suitable materials and suitable deposition techniques for the passivation and the metallization permits application at temperatures below 350xc2x0 C. This ensures that the defect region""s defects produced by the particle irradiation do not become depleted.
The process according to the invention is suitable for fabricating all semiconductor components in which the carrier lifetime needs to be adjusted very accurately. It is suitable, in particular, for fabricating diodes which are to be irradiated on the anode side.